The present invention relates to a process for marking the surface of an item made from a silica-based material, such as the glass body of a light bulb.
During the manufacture of a light bulb that comprises a glass body, for example in the form of a tube, an identifying mark is generally placed on an element of the bulb.
This mark comprises, for example in the form of typographical characters, details of the technical characteristics of the bulb, of the name of the manufacturer, etc, which allow easy identification of each model of bulb, in particular during packaging, during installation and during replacement.
The mark represents a style of writing that must in particular be legible and easy to identify on the tube.
The glass tubes of some light bulbs, such as halogen type bulbs, reach very high operating temperatures, for example of the order of 800xc2x0 C.
The inks for marking the glass are not resistant to these high temperatures. They are generally intended to withstand a maximum constant temperature of 500xc2x0 C.
As a result, as it is not possible to apply a mark directly to the glass body of the bulb, a support is provided, generally of a ceramic material, that is an integral part of the glass tube and on which the marking ink is deposited.
As the temperature of the ceramic support remains well below the temperature of the glass tube, when the light bulbs operates normally, the heat produced by the tube does not degrade the ink which is then subject to a temperature close to that of the ceramic, for example 300xc2x0 C.
However, the use of a ceramic support increases the manufacturing cost of the light bulb.
Moreover, mounting the support on the glass tube and marking it require special steps during the tube manufacturing process, which makes the manufacturing process complex and increases the manufacturing time.
Another disadvantage of the support is its size.
The invention aims to overcome these disadvantages by proposing a marking process that allows the application of a marking product directly to an outer surface of the glass body of the light bulb, without the need to provide a support.
To this end, the invention proposes a process for marking a surface of an item made from a silica-based material, characterized in that it includes the following steps:
creation of a mark on said surface by depositing a marking product made from a substantially homogenous mixture of an ink and a silica powder;
vitrification of the marking product on said surface by heating to a very high temperature.
According to other characteristics of the invention:
the marking product is deposited on the surface of the item prior to the final forming of said item, which final forming operation comprises a phase in which it is heated to a very high temperature, which causes the vitrification of the marking product onto the surface of the item;
the item is broadly in the form of a rectilinear tube before its final forming, with the final forming of the item comprising a so-called bending phase during which the item is heated to a very high temperature with a view to being bent, and said vitrification of the marking product is obtained during the bending phase;
the marking product is deposited on the surface of the item by means of an inking pad that is intended to take the marking product from an engraved imprint representing the motif of the mark;
the marking product comprises a diluent;
the marking product comprises a hardener;
the marking product is prepared by mixing in a homogenous fashion, according to proportions by weight, approximately 81% ink, 3% silica powder, 12% diluent and 4% hardener.
The invention also proposes a marking product for the implementation of the process in accordance with the invention, characterized in that it comprises a substantially homogenous mixture of ink and silica powder.